FROTH: Fundamentals and Reliability of Offshore Structure Hydrodynamics

Lead Research Organisation: City, University of London
Department Name: Sch of Engineering and Mathematical Sci

Abstract

The FROTH project is a close collaboration between five universities with significant experience in research into wave interactions with fixed and floating structures working together to combine and apply their expertise to different aspects of the problem. The aim is to investigate the detailed physics of violent hydrodynamic impact loading on rigid and elastic structures through a carefully integrated programme of numerical modelling and physical experiments at large scale. Open source numerical code will be developed to simulate laboratory experiments to be carried out in the new national wave and current facility at the UoP [http://www.plymouth.ac.uk/pages/view.asp?page=34369].
It is well known that climate change will lead to sea level rise and increased storm activity (either more severe individual storms or more storms overall, or both) in the offshore marine environment around the UK and north-western Europe. This has critical implications for the safety of personnel on existing offshore structures and for the safe operation of existing and new classes of LNG carrier vessels whose structures are subject to large instantaneous loadings due to violent sloshing of transported liquids in severe seas. Some existing oil and gas offshore structures in UK waters are already up to 40 years old and these aging structures need to be re-assessed to ensure that they can withstand increased loading due to climate change, and to confirm that their life can be extended into the next 25 years. The cost of upgrading these existing structures and of ensuring the survivability and safe operation of new structures and vessels will depend critically on the reliability of hydrodynamic impact load predictions. These loadings cause severe damage to sea walls, tanks providing containment to sloshing liquids (such as in LNG carriers) and damage to FPSOs and other offshore marine floating structures such as wave energy converters.
Whilst the hydrodynamics in the bulk of a fluid is relatively well understood, the violent motion and break-up of the water surface remains a major challenge to simulate with sufficient accuracy for engineering design. Although free surface elevations and average loadings are often predicted relatively well by analysis techniques, observed instantaneous peak pressures are not reliably predicted in such extreme conditions and are often not repeatable even in carefully controlled laboratory experiments. There remain a number of deeply fundamental open questions as to the detailed physics of hydrodynamic impact loading, even for fixed structures and the extremely high-pressure impulse that may occur. In particular, uncertainty exists in the understanding of the influence of: the presence of air in the water (both entrapped pockets and entrained bubbles) as the acoustic properties of the water change leading to variability of wave impact pressures measured in experiments; flexibility of the structure leading to hydroelastic response; steepness and three dimensionality of the incident wave.
This proposal seeks to directly attack this fundamentally difficult and safety-critical problem with a tightly integrated set of laboratory experiments and state of the art numerical simulations with the ultimate aim of providing improved guidance to the designers of offshore, marine and coastal structures, both fixed and floating.

Publications

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Ma Q.W. (2015) Numerical and experimental studies of Interaction between FPSO and focusing waves in Proceedings of the International Offshore and Polar Engineering Conference

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Ma Q.W. (2013) Fully nonlinear simulation of resonant wave motion in gap between two structures in Proceedings of the International Offshore and Polar Engineering Conference

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Sriram V (2014) A hybrid method for modelling two dimensional non-breaking and breaking waves in Journal of Computational Physics

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Yan S. (2014) Sensitivity investigation on wave dynamics with thin-walled moonpool in Proceedings of the International Offshore and Polar Engineering Conference

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Yan S. (2013) Fully nonlinear simulation of tsunami wave impacts on onshore structures in Proceedings of the International Offshore and Polar Engineering Conference

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Yan S. (2015) Numerical and experimental studies of moving cylinder in uni-directional focusing waves in Proceedings of the International Offshore and Polar Engineering Conference

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Yang H. (2014) Preliminary numerical study on oil spilling from a DHT in Proceedings of the International Offshore and Polar Engineering Conference

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Zhou J.T. (2014) Comparative studies on numerical simulation of tsunami wave loads on 3D onshore structures in Proceedings of the International Offshore and Polar Engineering Conference

 
Description This is a part of collaborative project. The task at City is to develop methodology for generating multiple directional wave groups propagating in different directions and methodology for modelling interaction between wave impact and response of floating bodies. The main achievements include:
1) Develop a method for modelling 3D nonlinear directional waves by improving the Spectral Boundary Integral Method for simulating nonlinear water waves.

2) Develop a hybrid method for modelling 2D Non-breaking and Breaking Waves. This is first paper to present a hybrid method coupling a meshless method based on the Navier Stokes (NS) equations, with a finite element method (FEM) based on the fully nonlinear potential flow theory (FNPT) in order to efficiently simulate the violent waves and their interaction with marine structures.

3) Numerical and Experimental Studies of Interaction between FPSO and Focusing Waves and hydrodynamics in gap between two Structures.


3)
Exploitation Route The new 3D method for modelling 3D nonlinear directional waves have been used for developing another method, called Enhanced Spectral Boundary Integral (ESBI) method for modelling fully nonlinear wave-current interactions, which is more efficient to model directional waves in a relative large domain.

The idea of hybrid method developed in this project has been adopted by other researchers and have been extended to solve 3D wave-structure interaction problems.
Sectors Energy,Environment,Transport

 
Description Not yet now but we are working together with Livermore Software Technology Corporation to combine our QALE-FEM code with their commercial software to deal with interaction between waves and structures. The above was stopped. We are now working on combining QALE-FEM with OpenFOAM and will consider to release a open source code. The method developed in this project have been adopted and extended by other researchers and projects.
Sector Energy,Environment,Transport
Impact Types Societal,Economic

 
Description A CCP on Wave/Structure Interaction: CCP-WSI
Amount £472,393 (GBP)
Funding ID EP/M022382/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 10/2015 
End 09/2020
 
Description A Zonal CFD Approach for Fully Nonlinear Simulations of Two Vessels in Launch and Recovery Operations
Amount £348,022 (GBP)
Funding ID EP/N008863/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 01/2016 
End 12/2018
 
Description A novel integrated approach to efficiently model viscous effects on wave-structure
Amount £100,106 (GBP)
Funding ID EP/N006569/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 11/2015 
End 11/2017
 
Title QALE-FEM method for modelling nonlinear water waves 
Description The EPSRC projects have helped development of QALE-FEM method for modelling nonlinear water waves, which is much more efficient compared with other methods based on the same theory, i.e., the fully nonlinear potential theory. 
Type Of Material Physiological assessment or outcome measure 
Year Produced 2015 
Provided To Others? Yes  
Impact The code and methods have been provided to research partners in 2015. It was also installed on a machine of DNV GL Noble Denton, which is a large company in the marine engineering. They will test it and give us feedback in due course. 
 
Description Collaberation with SUTGEF 
Organisation Society for Underwater Technology
Department SUT Group on Environmental Forces (SUTGEF)
Country United Kingdom 
Sector Learned Society 
PI Contribution I together with other project investigators had organised two open workshops with SUTGEF (Group on Environmental Forces of Society for Underwater Technology, and my team member made two presentations in the workshop.
Collaborator Contribution SUTGEF (Group on Environmental Forces of Society for Underwater Technology) draw the attention of his members to the workshops, which include experts from industries and academics.
Impact Two workshops jointly organised.
Start Year 2014
 
Description Collaboration with Lloyd's Register 
Organisation Lloyd's Register
Country United Kingdom 
Sector Charity/Non Profit 
PI Contribution Lloyd's Register contribute to a PhD studentship. Lloyd's Register will not only make financial contribution but also help supervise the student.
Start Year 2012
 
Title Framework for combing the OpenFoam and our QALE-FEM codes 
Description This framework is for combing the OpenFoam and our QALE-FEM codes, and shared within the group of project investigators. 
Type Of Technology Software 
Year Produced 2015 
Open Source License? Yes  
Impact Not yet and project investigators just started to use it.